The present invention relates to an antilocking control system for vehicles in which control signals for controlling a pressure regulating unit associated with two wheels or two groups of wheels are produced in an evaluating circuit from the signals of sensors associated with different wheels or groups of wheels when a wheel shows a tendency to lock (select-low) and at times when both monitored wheels show a tendency to lock (select-high).
Antilocking control devices of the above-mentioned type are known, for example, from U.S. Pat. No. 3,535,004, issued Oct. 20, 1970 to D. W. Howard et al. In this patent the control channel normally receives the voltage corresponding to the slower rotating vehicle wheel (select-low). A switch to select-high regulation, i.e., the feeding of the voltage corresponding to the speed of the faster rotating wheel, is actuated if and as long as the wheels rotate at significantly different speeds, i.e., are on ground having significantly different coefficients of friction. On such ground, the one wheel, with select-low control, would contribute only insignificantly to the braking effort. The known arrangement serves the purpose of saving control channels so as to reduce the cost of the antilock control system.
German Offenlegungsschrift No. 2,119,590 corresponding to U.S. Pat. No. 3,797,892, issued Mar. 19, 1974 to H. Leiber et al discloses, for common control of the brake pressure, a switch from the normally effective select-high mode of control to the select-low mode of control whenever transverse accelerations occur or are to be expected. In this case the drawbacks of the select-high mode of control are to be eliminated when braking in curves.
German Offenlegungsschrift No. 2,243,260 corresponding to U.S. Pat. No. 3,907,378, issued Sept. 23, 1975, to H. Leiber et al finally discloses normal operation with select-low and a switch to select-high, for a given period of time, a given period after the occurrence of a control signal so that here, too, the pressures at two wheel brakes are controlled together.